In the art of packaging, typically a sealed plastic package must be torn, cut, or otherwise broken into in order to obtain access to the contents thereof.
Particularly in the field of plastic packaging, or of packaging incorporating plastic film, heat sealed interfaces between thermally bondable plastic layers typically are either so tightly fused together as not to be delaminatable or peelable without film rupture, or, alternatively, the film interfacial bonding is so poor as not to provide the required sealing action and seal bond strength required for commercial purposes, particularly in the case of perishable food stuffs.
Particularly, in the latter case, the package wall structure is important so that the provision of an effectively sealed package with a truly peelable seal is difficult to achieve and still have a container which is also adapted for wide spread commercial utilization.
The idea of achieving a peelable seal seemingly has become even more difficult to achieve with the significant commercial usage of packaging films comprised of ethylene acid copolymers (including ionomers) which are characterized, among other properties, with good toughness and outstanding adhesion to a variety of substrates including metals (such as aluminum foil). Particularly in composite (e.g. laminate) structures, ionomer layers commonly serve as heat seal layers which bond well and irreversably to themselves.
It is believed that ethylene acid copolymers (including probably ionomers) have been polyblended with certain other resins and formed into films for the purpose of providing products which would retain the desirable toughness and bonding characteristics of such copolymers and which would also provide peelability for ease in package opening. However, such polyblends appear to suffer from certain disadvantages. For one thing, the resulting polyblend films can have sealing problmes caused by the weakened capacity of such films to form commercially acceptable heat seals with other films. For another thing, it is sometimes difficult to retain the desired toughness properties in the resulting polyblended film. Other problems and disadvantages also exist.
The packaging art needs improved means for producing durable heat seals between ethylene acid copolymer (including ionomer) films and other films and still have the resulting seals be peelable.